Post-Diet Weight Gain Blamed on Change in Body

Interestingly, the effect worked in the opposite direction as well. A 10% increase in body weight was accompanied by a 15% increase in food intake necessary to maintain the new weight. "This is a subtle difference," Leibel said. "It wouldn't have been observed" in people who were not hospitalized.

The results support the now widely accepted idea that each individual has a genetically determined set point, a metabolically "desired" weight that the body goes to great lengths to maintain. Researchers are looking for ways to change the set point permanently, he added, but have been unsuccessful.

The researchers also observed that at least in terms of controlling weight, what a person eats is irrelevant. "A low-fat diet may be healthful for a number of other reasons," Leibel said, "but a calorie of fat and a calorie of carbohydrate count the same in weight reduction." Unfortunately, 500 calories of junk food is not nearly as filling as 500 calories of vegetables. Food high in fat also tastes better, so you are more likely to eat more, he added.

"The take-home message," he said, "is that (obesity) is not a question of willpower or behavior. Maintenance of a new body weight will require indefinite attention to caloric intake. You will have to restrict calories . . . 15% more than we thought before. And you are also going to have to get more exercise."